June 15, 2009 -- Skipping breakfast is often a big no-no if you are trying to lose or maintain weight because it leads to high-calorie cravings later. Now researchers think they know why that happens.

Forgoing the first meal of the day actually tricks your brain into thinking you want higher-calorie foods -- foods that can make you fat, or at least increase your risk for weight gain.

A team from Imperial College London presented the news at the Endocrine Society's 91st annual meeting in Washington, D.C. The researchers used a scan called functional magnetic resonance imaging (fMRI) to look at how feeding behaviors affected the brain's "reward" center, which plays a role in pleasures and the body's response to them.

Functional MRI allows doctors to look at how blood flow increases in response to brain activity.

The study involved 20 healthy, non-obese people. They skipped breakfast before the fMRI exam. During the test, they looked at random photos of high- and low-calorie foods. The high-calorie foods included pizza, cake, and chocolate. The healthier options included vegetables, fish, and salad.

The brain's reward center lit up more vividly, or became more active, when the person saw a high-calorie food as opposed to a low-calorie choice. (The taste and smell of food can also activate the brain's reward center.)

However, when the participants ate breakfast and had the same test repeated 90 minutes after eating breakfast, the brain's reward center did not show any significantly greater activity when shown the high-calorie photos.

The study participants also rated how appealing they found each food picture. When skipping breakfast, high-calorie foods topped the list of favorites. After eating, however, the group did not show a strong preference for the calorie-laden foods. Their choices corresponded with the MRI findings.

Breakfast has long been touted as the most important meal of the day, and researchers say their findings add credence to that adage.

"Our results support the advice for eating a healthy breakfast as part of the dietary prevention and treatment of obesity," Tony Goldstone, MD, PhD, a consultant endocrinologist with the MRC Clinical Sciences Centre at Imperial College London, says in a statement. "When people skip meals, especially breakfast, changes in brain activity in response to food may hinder weight loss and even promote weight gain."

Researchers hope the findings could one day lead to the development of weight loss medications that target the brain's reward circuitry and disrupt the craving bias between high-calorie and low-calorie foods.